Weird fermentation?

So I brewed a higher gravity porter (1.065) and used Wyeast 1056...I didn't have a starter, and I had an extra pouch of 1056 that I had forgot about that was still good...I dumped both smack packs in, and all went well for about 24 hours...after that the airlock fell silent...I swirled the bucket without splashing to rouse the yeast and I have had some slow bubbling for about 10 hours now.

My question is...did I overpitch? Is there another reason it could have gotten stuck? The temp hasnt fluctuated but maybe 1 or 2 degrees around 71 degrees.

The packs say they're good for five gallons at 1.060 so I wouldn't expect the pitch rate to mess up your beer. Usually it just gets done faster in that situation. I've had a couple ferment down almost completely in 24 hours before. Keep in mind your airlock isn't a good indicator of the volume of activity inside and it's not an accurate measuring device. Check it with your hydrometer and see if it's done.